SLVSDX2A September   2017  – December 2017 TPS23521

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Typical Characteristics
  7. 7 Parameter Measurement Information
    1. 7.1 Relationship between Sense Voltage, Gate Current, and Timer
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Current Limit
        1. 8.3.1.1 Programming the CL Switch-Over Threshold
        2. 8.3.1.2 Setting Up the PROG Pin
        3. 8.3.1.3 Programming CL1
        4. 8.3.1.4 Programming CL2
      2. 8.3.2 Soft Start Disconnect
      3. 8.3.3 Timer
      4. 8.3.4 Gate 2
    4. 8.4 Device Functional Modes
      1. 8.4.1 OFF State
      2. 8.4.2 Insertion Delay State
      3. 8.4.3 Start-up State
      4. 8.4.4 Normal Operation State
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Selecting RSNS
        2. 9.2.2.2 Selecting Soft Start Setting: CSS and CSS,VEE
        3. 9.2.2.3 Selecting VDS Switch Over Threshold
        4. 9.2.2.4 Timer Selection
        5. 9.2.2.5 MOSFET Selection and SOA Checks
        6. 9.2.2.6 EMI Filter Consideration
        7. 9.2.2.7 Under Voltage and Over Voltage Settings
        8. 9.2.2.8 Choosing RVCC and CVCC
        9. 9.2.2.9 Power Good Interface to Downstream DC/DC
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Community Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.3.1 Current Limit

The TPS23521 utilizes two current limit thresholds:

  • ICL1 – also referred to as high current limit threshold, which is used when the VDS of the hot swap FET is low.
  • ICL2 – lower current limit threshold, which is used when the VDS of the hot swap FET is high.

This dual level protection scheme ensures that the part has a higher chance of riding out voltage steps and other transients due to the higher current limit at low VDS, while protecting the MOSFET during start into short and hot-short events, by setting a lower current limit threshold for conditions with high VDS. The transition threshold is programmed with a resistor that is connected from the drain of the hot swap FET to the D pin of the TPS23521. The figure below illustrates an example with a ICL1 set to 25 A and ICL2 set to 3 A. Note that compared to a traditional SOA protection scheme this approach allows better utilization of the SOA in the 10 V < VDS.< 40-V range, which is critical in riding through transients and voltage steps.

Note that in both cases the TPS23521 regulated the gate voltage to enforce the current limit. However, this regulation is not very fast and doesn’t offer the best protection against hot-shorts on the output. To protect in this scenario a fast comparator is used, which quickly pulls down the gate in case of severe over current events (2x bigger than VCL1).

TPS23521 tps23523_dual_current_limit_vs_FET_.gifFigure 7. Dual Current Limit vs FET Power Limit